SOI Isolation Region Layout for Uniform Replacement Gate FETs
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Solution Overview
Problem
In integrated circuit (IC) manufacturing, raised source/drain structures with variable dimensions at the boundary between field effect transistors (FETs) and shallow trench isolation (STI) regions lead to non-uniformities, increasing FET threshold voltage variability, delay, and leakage, which degrades IC performance and power efficiency.
Innovation Solution
The implementation of isolation regions that extend through the top silicon layer to the buried oxide layer in a silicon-on-insulator substrate, replacing traditional STI regions, using a block mask to selectively remove active silicon and form isolation trenches filled with insulating material, minimizing capacitance penalty and allowing for higher device density and lower capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If isolation regions are included to eliminate boundary non-uniformity, then FET threshold voltage variability is reduced, but device density decreases and wiring space is limited
Solution Approach 1:
The patent divides the isolation structure into two distinct parts: shallow trench isolation (STI) regions that provide electrical isolation between devices, and separate isolation regions that specifically address boundary non-uniformity. This segmentation allows the STI to be minimized for high density while dedicated isolation regions handle the precision requirement, resolving the contradiction between uniformity and device density.
Solution Approach 2:
The patent applies different isolation structures at different locations: standard STI is used in bulk areas where density is critical, while enhanced isolation regions are placed specifically at gate-STI boundaries where non-uniformity occurs. This local differentiation maintains high device density overall while providing precision isolation exactly where needed.
2Manufacturing precision
If isolation regions are included to eliminate boundary non-uniformity, then FET threshold voltage variability is reduced, but wiring space is limited
Solution Approach 1:
By separating the isolation function into STI regions for bulk isolation and smaller dedicated isolation regions for boundary control, the patent reduces the total isolation area compared to requiring isolation regions everywhere. This segmentation preserves more wiring space while still achieving the required threshold voltage uniformity at critical boundaries.
Solution Approach 2:
The patent applies isolation regions only locally at gate-STI boundaries rather than universally across all STI regions. This localized approach provides the necessary precision isolation where it affects device performance while minimizing the total area consumed by isolation structures, thereby preserving wiring space.
3Object-generated harmful factors
If isolation regions are included to eliminate boundary non-uniformity, then leakage is reduced, but load capacitance increases
Solution Approach 1:
The patent segments the isolation functionality so that STI provides the primary electrical isolation blocking leakage currents, while smaller isolation regions at boundaries provide additional leakage prevention where non-uniformity occurs. This segmentation reduces the total insulating material volume compared to comprehensive isolation regions, thereby reducing load capacitance while maintaining leakage control.
Solution Approach 2:
By placing isolation regions only at critical gate-STI boundaries rather than across all STI regions, the patent provides leakage prevention exactly where boundary non-uniformity causes problems while minimizing the total capacitance added by isolation structures. This local quality approach balances leakage reduction with capacitance minimization.
4Reliability
If STI regions are used for electrical isolation, then device isolation is achieved, but boundary non-uniformity increases
Solution Approach 1:
The patent divides the isolation system into STI regions that provide the fundamental electrical isolation function and separate isolation regions that specifically address boundary uniformity. This segmentation allows each component to be optimized for its specific function: STI for reliable isolation and boundary isolation regions for uniformity control.
Solution Approach 2:
The patent enhances the quality of isolation specifically at gate-STI boundaries by adding isolation regions at these critical locations, while maintaining standard STI in bulk areas. This local quality enhancement ensures reliable electrical isolation overall while providing superior boundary uniformity where it most impacts device performance.
Data Source
AI summary
A semiconductor structure includes a silicon-on-insulator (SOI) substrate, the SOI substrate comprising a bottom silicon layer, a buried oxide (BOX) layer, and a top silicon layer; a plurality of active devices formed on the top silicon layer; and an isolation region located between two of the active devices, wherein at least two of the plurality of active devices are electrically isolated from each other by the isolation region, and wherein the isolation region extends through the top silicon layer to the BOX layer.